Radio-Frequency Identification (RFID) tags have received substantial attention because of their potential for allowing inventory control or checkout scanning without the need for separate scanning of each tagged article or item in a group of items. Tagging allows an item to be associated with relevant information such as nature of the item, price, serial number, expiration date, andor shipping date. Among the problems which have confronted designers has been the need to report or respond with a plurality of bits when interrogated. In general, this requires some sort of memory in which the bits representing the item with which the tag is associated are stored. This requirement, in turn, requires either a nonvolatile memory or a volatile memory in conjunction with a power source. In the case of a volatile memory with a battery power source, the tag undesirably loses its information if the battery should fail. If a nonvolatile memory is used, the reading of the nonvolatile memory can itself require power, so some internal or external source of energy must be provided, which undesirably increases the cost of the tags. Some RFID tags are active, but do not require an on-board power source, as they are energized by the interrogating electromagnetic wave. However, the power level of the radiated electromagnetic field required for such activation may undesirably interfere with other radio-frequency devices such as communications and control devices in the region. Thus, the interrogating radio-frequency field should be of low amplitude, which in general is not compatible with the powering of an active RFID tag.
Those skilled in the art know that the term “radio frequency” originally referred to frequencies which are within the range now known as Very Low Frequency (VLF), ranging from about 3 to 30 KHz. With the advent of broadcast services in the frequency range of 540 to 1600 KHz, the term came to include such frequencies. With the passage of time and the expansion of the range of usable frequencies of electromagnetic radiation the term has come to relatively broadly encompass all frequencies of electromagnetic radiation below light frequencies.
Inkode Corporation, whose United States address is Inkode USA, 8230 Old Courthouse Road, Vienna, Va. 22182 has for some years licensed the manufacture of low-cost RFID tags to manufacturers, such as Lintec Corporation. These tags include reflective antenna-like elements with dimensions as small as 250 angstroms (Å) imbedded in the dielectric material of the tag. In one version, the reflective elements, termed “taggents,” are contained within an ink which is applied to the tag. Each of the reflective elements reflects electromagnetic energy at a frequency related to its dimensions. Multiple reflective elements imbedded in a tag can result in a spectral response which is different from the spectral responses of other tags having reflective elements of different lengths.
One of the advantages of the reflective RFID tags licensed by Inkode is that they are inexpensive, and can respond to an interrogating signal from a significant distance, which may be as great as 40 feet at the current state of the art. In addition, RFID tags are desirable in that the radio-frequency interrogating electromagnetic energy, and the reflective responses thereto, can pass through dielectric materials and through some regions which include both dielectric and electrically conductive materials. As a result of these features, an electromagnetic “scanner” corresponding to a bar-code scanner at a checkout counter would not necessarily have to have a direct view of a tagged item in order to detect its presence. This, in turn, could result in a checkout procedure in which a cart, of goods is wheeled up to the checkout counter, and the items in the cart are “immediately” identified without removal or discrete scanning. The saving in checkout time and the reduction in clerk activity could be very beneficial in such situations.
Improved RFID tags and consequent improved checkout and inventory procedures are desired.